Electrolysis, as used for common red or brown rust removal, is not a reducing of ferrous oxide to ferric oxide. Common red rust IS ferric oxide, or more accurately, hydrated ferric oxide, Fe2O3.nH2O. The black slime that can be rubbed off the surface of the formerly rusted item after electrolysis is mostly a mixture of iron metal and magnetite, Fe3O4, another oxide of iron... also known as ferro- ferric oxide. This is the same black oxide that forms during the boiling conversion during slow rust bluing. But due to the electric current, it is not bound to the parent metal.
I personally like using the molasses/water solution method of rust removal. It is slow, but very cheap and very effective, without any damage to the sound metal. I just pulled a complete bolt action I recently bought, from my bucket of molasses slop. Scrubbed it off and rinsed it to find that it was totally free of rust, inside and out. The electrolysis method needs an internal anode to effectively remove rust on the insides of items. It took a couple weeks, and since the solution can be re-used many times, it probably cost less than a nickel to clean.
When the molasses solution finally does quit working, you just dump it on your lawn or shrubs. No toxic mess to deal with, and no concentration of explosive gasses. I always keep a 5 gallon bucket of it in my garage, and suspend rusty auction and flea market finds in it. I can forget about them without any fear of damage. The smell is not anywhere near as objectionable as you read about on the internet. I wish I had learned about it years ago.
